Image display

ABSTRACT

The present invention is an image display apparatus having pixels PXLs arranged in a matrix form, and comprises a display panel displaying images by reflecting external light from the front side or by having illumination light from the back side transmit therethrough, and a flat-type back light arranged at the back of the display panel and radiating the illumination light. Each pixel PXL is divided on a flat surface into a reflection area R for reflecting the external light incident from the front side of the display panel to display an image and a transmission area T for transmitting the illumination light incident from the back side of the display panel to display an image. The back light is a flat type, with layers consisting of electrodes ( 204 ), ( 202 ) and a luminescent layer ( 203 ) sandwiched inbetween being formed on a substrate ( 201 ), and radiates the illumination light generated from the luminescent layer ( 203 ) toward the transmission area T of each pixel PXL when voltage is applied between the electrodes ( 204 ), ( 202 ).

TECHNICAL FIELD

The present invention relates to a, so to speak, hybrid-type imagedisplay apparatus provided on the back with a reflective layer on a partof which is formed an opening (hereinafter, sometimes called asemi-transmission reflective layer).

BACKGROUND OF THE INVENTION

A hybrid-type display apparatus is disclosed e.g. in a Japanese patentlaid-open No. 11-52366 and a Japanese patent laid-open No. 11-183892.The hybrid-type image display apparatus performs a reflective displayusing external light by reflecting on a semi-transmission reflectivelayer on the back side the external light incident from the front sidewhen the external light having sufficient brightness (such as naturallight or interior light) is obtained, and performs a transmittivedisplay using illumination light which is a back light arranged on theback side of the image display apparatus when the external light havingsufficient brightness is not obtained. This hybrid-type image displayapparatus basically comprises a display panel having pixels arranged ina matrix form and displaying images by reflecting external light fromthe front side or by having illumination light from the back sidetransmit therethrough, and a flat-type back light arranged at the backof the display panel and radiating the illumination light.

Such a hybrid-type image display apparatus is preferably appliedparticularly to a display section of a portable information terminaldevice or a portable telephone terminal device. As the external lightcan be used when it is bright around, it is not necessary to turn on theback light, and thus electric power consumption can be reduced. In theportable information terminal device or the portable telephone terminaldevice in which electric power supply is limited, it is the mostimportant point to reduce the electric power consumption.

Conventionally, an LED or a fluorescent tube is used as the back light.Accordingly, the thickness of the back light cannot be 2 mm or thinner.Although there will be raised an increasing demand for reducing thethickness of a portable device in the future, the conventional backlight cannot satisfy the demand of reducing its thickness. Thus, thereis a need for newly developing a back light structure suitable for ahybrid-type image display apparatus. Meanwhile, an EL is used as aconventional back light, as well as the LED or the fluorescent tube, andsuch a back light is disclosed in a Japanese patent laid-open No.11-316376. The art disclosed in this laid-open patent is not used in ahybrid-type image display apparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new image displayapparatus that can solve the technical problems that the above-mentionedconventional apparatuses have.

In order to solve the above technical problems, the present inventionprovides an image display apparatus comprising a display panel havingpixels arranged in a matrix form and displaying images by reflectingexternal light from the front side or by having illumination light fromthe back side transmit therethrough, and a flat-type back light arrangedat the back of the display panel and radiating the illumination light.Each pixel constituting this apparatus is divided on a flat surface intoa reflection area for reflecting the external light incident from thefront side of the display panel to display an image and a transmissionarea for transmitting the illumination light incident from the back sideof the display panel to display an image. The back light is a flat type,with layers consisting of electrodes and a luminescent layer sandwichedinbetween being formed on a substrate, and radiates the illuminationlight generated from the luminescent layer toward the transmission areaof each pixel when voltage is applied between the electrodes.

In the present invention, the luminescent layer is preferably composedof an organic electro-luminescent material. The shape of the layersconsisting of the electrodes and the luminescent layer sandwichedinbetween is manufactured to match that of the transmission area so thatthe luminescent light may be supplied only to the transmission area ofeach pixel. The display panel comprises a pair of upper and lowersubstrates to each of which is formed an electrode, and liquid crystalheld between the substrates. The back light has a polarizing layerdeposited on the layers consisting of the electrodes and the luminescentlayer sandwiched inbetween, and the liquid crystal displays an image,effected by the illumination light transmitted through the polarizinglayer.

In the present invention, a thin-film element using a self luminescentmaterial is used as a back light of the hybrid-type image displayapparatus. A self luminescent material is exemplified by an organicelectro-luminescent (EL) material. A luminescent layer of the organic ELis formed on a substrate. A glass substrate or the like can be used asthe substrate. On the glass substrate is formed a lower electrode, onwhich is deposited the luminescent layer made of the organic ELmaterial. Further, an upper electrode made of a transparentelectro-conductive film is formed on the luminescent layer such that theorganic EL film is sandwiched between the upper and lower electrodes.When voltage is applied between the upper and lower electrodes, currentflows in the luminescent layer, and the organic EL material illuminates.The flat-type back light prepared in such a process is 1 mm or thinnerin thickness, and is used attached to the back surface of the displaypanel. This back light may be arranged to a peripheral portion of theback surface of the display panel. The organic EL radiates whileluminescent light depending on driving current, and can be used asillumination light. The shape of the material constituting the luminouselement is patterned to match that of the transmission area included ineach pixel formed in the display panel, to reduce unnecessaryluminescence. Thus, current consumption can be minimized.

Other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodiments andthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial cross-sectional view showing a basic structure ofan image display apparatus according to the present invention, and FIG.1B is a partial plan view of the apparatus.

FIGS. 2A to 2D are cross-sectional views showing a method formanufacturing a back light incorporated in the image display apparatusshown in FIG. 1 in a process order.

FIG. 3 is a partial cross-sectional view showing a preferred embodimentof the image display apparatus according to the present invention.

FIG. 4 is a schematic view for explaining an operation of the imagedisplay apparatus shown in FIG. 3.

FIG. 5 is a perspective view showing a portable information terminaldevice to which the present invention is applied.

FIG. 6 is a plan view showing a portable telephone terminal device towhich the present invention is applied.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Preferred embodiment of the present invention will now be described withreference to the drawings.

FIGS. 1A and 1B are schematic views showing a basic structure of ahybrid-type image display apparatus according to the present invention.

The hybrid-type image display apparatus basically comprises a displaypanel having pixels arranged in a matrix form and displaying images byreflecting external light from the front side or by having illuminationlight from the back side transmit therethrough, and a flat-type backlight arranged at the back of the display panel and radiating theillumination light.

FIG. 1A shows a cross-sectional structure of the apparatus for a pixel.As shown in the figure, the display apparatus comprises a display panelhaving a pair of substrates 1, 2 at the front and back arranged to faceto each other. On the inner surface of one substrate 1 is formed oneelectrode 10, and on the inner surface of the other substrate 2 isformed the other electrode 11. At a portion where the one electrode 10and the other electrode 11 face to each other is formed a pixel. A colorfilter CF is provided on the front substrate 1 to match the pixel.Between the pair of the substrates 1, 2 at the front and back is held,for example, a liquid crystal layer 3 as an electronic optical layer.This liquid crystal layer 3 is a guest-host liquid crystal, and blocksthe incident light or lets the incident light pass therethrough per apixel, in response to the voltage applied between the electrodes 10 and11.

It is to be noted that the electronic optical element of the presentinvention is not limited to the liquid crystal, but may be anotherelectronic optical element. The liquid crystal is not limited to aguest-host liquid crystal, but may be a liquid crystal of another mode.

On the back substrate 2 is provided a reflective layer 8. The reflectivelayer 8 has an opening H for each pixel, and divides each pixel into atransmission area T inside the opening and a reflection area R outsidethe opening on a flat surface. In the present embodiment, the reflectivelayer 8 is composed of a metal film formed on the convexoconcave surfaceof the substrate 2 and also works as the above-mentioned electrode 11.Also, on the transmission area T is formed a transparentelectro-conductive film such as an ITO, which serves both as theabove-mentioned opening and as the electrode 11. As apparent from theabove description, the electrode 11 formed on the substrate 2 has ahybrid structure having the metal film provided in the reflection area Rand the transparent electro-conductive film provided in the transmissionarea T in the present embodiment.

The color filter CF is composed of a colored layer 50 and a transparentlayer 51. The colored layer 50 is thinner in the reflection area R thanin the transmission area T. The transparent layer 51 is formed to fillthe gap of the colored layer 50 generated between the transmission areaT and the reflection area R. More specifically, the transparent layer 51is composed of a transparent resin film formed on the inner surface ofthe front substrate 1, and the colored layer 50 is composed of a coloredfilm formed piled on the transparent resin film. The thickness of thetransparent layer 51 is set to the optimum one to adjust the opticaldensity of the colored layer 50 both in the transmission area T and inthe reflection area R.

As described above, in the hybrid-type display apparatus, a transparentresin film such as an acrylic resin is selectively formed only on thereflection area R by a method such as photo-lithography, and the coloredlayer 50 is layered on the transparent resin film. In the transmissionarea T, incident light (back light) passes once through the color filterCF having enough thickness normally, thus to obtain desired colorreproducibility. In the reflection area R, incident light (externallight) passes twice back and forward through the color filter CF havinglower optical density due to the intervention of the transparent resinfilm, thus to obtain desired color reproducibility. In this case, as thecolored layer 50 in the reflection area R is thin in thickness, theexternal light is not extremely absorbed regardless of passing twicethrough the color filter CF, but can maintain high reflectance and thusmaintain the brightness of the screen at a practical level.

On the back surface side of the display panel structured as above ismounted a flat back light. This back light shapes flat, having layersconsisting of electrodes 204, 202 and a luminescent layer 203 sandwichedinbetween, formed on a substrate 201 made of a glass board or the like.These layers are protected by a transparent protective layer 205. Thelower electrode 202 is made of a metal film, and the upper electrode 204is made of a transparent electro-conductive film such as an ITO. Whenthe voltage is applied between the upper electrode 204 and the lowerelectrode 202, the current flows in the luminescent layer 203 to obtainwhite illumination light. The illumination light is radiated toward thetransmission area T of each pixel. The luminescent layer 203 is made of,for example, an organic electro-luminescent material. The shape of thelayers consisting of the electrodes 204, 202 and the luminescent layer203 sandwiched inbetween is processed to match that of the transmissionarea T so that the illumination light may be radiated only to thetransmission area T of each pixel. As a result, unnecessary luminescenceis prevented, and current consumption is reduced. In the presentembodiment, the shape of the upper electrode 204 is patterned to matchthe shape of the transmission area T. Generally, at least one layer ofthe lower electrode 202, the luminescent layer 203 and the upperelectrode 204 may be patterned to conform with the shape of thetransmission area T.

FIG. 1B is a schematic view showing a flat shape of the image displayapparatus according to the present invention. As shown in the figure,pixels PXLs are partitioned in a matrix form by a black matrix BM. Eachof the pixels PXLs is divided on a flat surface into a transmission areaT at the center and a reflection area R around the transmission area Ton a flat surface, and has a, so to speak, hybrid structure. To conformwith this flat division, the aforementioned back light is patterned, anda substantial luminescent area of which is formed on the portion thatmatches the transmission area T. Also, the color filter is patterned toapproximately correspond to each of the pixels PXLs partitioned by theblack matrix BM.

Next, an example of a method for manufacturing the back light shown inFIG. 1 will be described with reference to FIGS. 2A to 2D.

Firstly, as shown in FIG. 2A, a substrate 201 made of a glass substratewhose thickness is 0.5 mm or thinner is prepared, on which is entirelyformed a lower electrode 202 made of an aluminum or the like. Thereflectance of the lower electrode 202 is preferably high. Next, asshown in FIG. 2B, a luminescent layer 203 made of, for example, anorganic EL material is deposited on the lower electrode 202 by vacuumdeposition. Subsequently, as shown in FIG. 2C, a transparentelectro-conductive film such as an ITO is deposited on the luminescentlayer 203 and is patterned in a predetermined shape to be an upperelectrode 204. The upper electrode 204 is patterned to correspond to thetransmission area included in each pixel on the display panel side.Alternatively, the luminescent layer 203 may be patterned instead of theupper electrode 204. Lastly, as shown in FIG. 2D, the layers composed ofthe luminescent layer 203 and the upper and lower electrodes 204, 202are covered with a protective film 205. As the protective film, aninsulating film such as a silicon dioxide may be used.

The total thickness of the back light structured as above can be 1 mm orthinner, and thus is a half of the thickness of the conventional LEDback light. Also, with respect to luminous efficiency, the organic ELmay possibly be greater than the LED.

FIG. 3 is a partial cross-sectional view schematically showing the imagedisplay apparatus according to the present invention for one pixel.

This image display apparatus comprises a hybrid-type liquid crystalpanel 100 and a flat-type back light 200. The present embodiment adoptsactive matrix-type pixels and uses the liquid crystal panel 100 of anECB (Electrically Controlled Birefringence) mode. That is, the ECB modeis one for controlling incident light to pass or be blocked by usingbirefringence of the liquid crystal. As an active element for drivingthe active matrix-type pixels, a thin-film transistor is used.

As shown in FIG. 3, a polarizing plate 40 and a ¼ wavelength plate 9 aremounted on the outer surface of a front substrate 1. On the innersurface of the substrate 1 is formed a color filter CF formed by pilinga colored layer 50 and a transparent layer 51. A black matrix BM is alsoformed on the inner surface of the substrate 1 to partition the colorfilters CFs per a pixel. On the surface of the color filter CD and theblack matrix BM is provided a common electrode 10 commonly formed alongpixels. On the common electrode 10 is deposited an orientation film 107.Also, a liquid crystal layer 3 having birefringence is held below theorientation film 107, under which is provided a back substrate 2. Thesurface of the substrate 2 is covered with an orientation film 115. Theorientation film 115 orients the liquid crystal layer 3 horizontally,cooperating with the orientation film 107 of the front substrate 1.

The thickness of the liquid crystal layer 3 is set so that the length inthe transmission area Td may be twice as long as the length in thereflection area Rd, as shown in FIG. 3. Specifically, the Td correspondsto a half of the wavelength of incident light, and the Rd corresponds toa quarter of the wavelength of the incident light. Below the orientationfilm 115 is formed a pixel electrode 11. This pixel electrode 11 iscomposed of a transparent electro-conductive film such as an ITO, andforms an opening for the transmission area. A reflective layer 8 isformed, part of which is overlapped with the transparent electrode 11,with an insulating film 114 between the reflective layer 8 and thetransparent electrode 11. The reflective layer 8 is composed of a metalfilm formed on the convexoconcave surface of the insulating film 114 andis connected at the same electric potential as that of theabove-mentioned pixel electrode 11. Thus, the reflection film 8constitutes a part of the pixel electrode. Under the pixel electrode 11is formed a thin-film transistor 108. The thin-film transistor 108 is ina bottom gate structure and has layers of a gate electrode 116, a gateinsulating film 117 and a semiconductor thin film 118 layered from thebottom to the top. The semiconductor thin film 118 is composed of apolycrystalline silicon, and its channel area corresponding to the gateelectrode 116 is protected by a stopper 119 from the upper side. Thethin-film transistor 108 having such a bottom gate structure is coveredwith an interlayer insulating film 120. The interlayer insulating film120 has a pair of contact holes, through which a source electrode 121and a drain electrode 122 are electrically connected to the thin-filmtransistor 108. These electrodes 121 and 122 are made by patterninge.g., an aluminum. To the drain electrode 122 is connected theaforementioned pixel electrode 11. The reflective layer 8 is alsoelectrically connected to the drain electrode 122 through a contact hole112 formed on the insulating film 114. On the other hand, signal voltageis supplied to the source electrode 121.

On the substrate 2 at the back side of the liquid crystal panel 100having such a structure is mounted the flat-type back light 200. Theback light 200 has a layered structure by forming a lower electrode 202on a substrate 201 made of a glass board or the like, on which aluminescent layer 203 is deposited, and further on which an upperelectrode 204 is formed. The layers composed of the upper and lowerelectrodes 204, 202 and the luminescent layer 203 sandwiched inbetweenare covered with an insulating protective film 205 such as a silicondioxide. On the protective film 205 is deposited a polarizing film 241.This polarizing film 241 is a, so to speak, coat-type polarizing plate.That is, as a functional material is coated on the protective film 205,and a predetermined process is carried out on it, the polarizing layer241 that makes a polarizing effect on illumination light radiated fromthe luminescent layer 203 can be formed. On the polarizing layer 241 isformed a ¼ wavelength layer 219. The ¼ wavelength layer 219 is made ofe.g., a uniaxially oriented optical film and is attached on thecoat-type polarizing layer 241.

FIG. 4 schematically illustrates an operation of the image displayapparatus shown in FIG. 3, and specifically shows a structure of areflection area. In FIG. 4, the right side shows an off state ofapplying voltage in which light passes, and the left side shows an onstate of the applying voltage in which the light is blocked.

This reflective display apparatus comprises a polarizing plate 40, a ¼wavelength plate 9, a front substrate 1, a color filter CF, a commonelectrode 10, a liquid crystal layer 3 having birefringence, areflective layer 8 also working as a pixel electrode, and a backsubstrate 2 layered from the top to the bottom. In the off state, liquidcrystal molecules 4 are oriented horizontally, and the liquid crystallayer 3 functions as a ¼ wavelength plate. In the on state, the liquidcrystal molecules 4 shifts to a vertical orientation, and the liquidcrystal layer 3 ceases to function as the ¼ wavelength plate. In otherwords, in the off state, the liquid crystal layer 3 that functions asthe ¼ wavelength plate and the ¼ wavelength plate 9 are overlapped, andthey function as a ½ wavelength plate as a whole. As incident light isradiated back and forth through the panel in a case of a reflectivetype, the panel functions as a one wavelength plate. The one wavelengthplate lets the incident light transmitted therethrough back and forth tolet it radiated a radiation light as it is. Thus, the incident linearlypolarized light transmitted through the polarizing plate 40 reaches anobserver as the radiated linearly polarized light as it is, and a statein which light passes can be obtained. On the other hand, in the onstate, as the liquid crystal layer 3 ceases to function as a ¼wavelength plate, only the ¼ wavelength plate 9 plays its role. In acase of a reflective type, as incident light goes back and forth throughthe ¼ wavelength plate 9, the panel functions as a ½ wavelength plateafter all. The ½ wavelength plate turns the incident linearly polarizedlight by 90° to be made as radiated linearly polarized light. Thus, theincident linearly polarized light transmitted through the polarizingplate 40 is turned by 90°, made as the radiated linearly polarizedlight, and absorbed in the polarizing plate 40. Thus, a state in whichlight is blocked can be obtained.

Meanwhile, the operation of the transmission area is similar to that ofthe above-mentioned reflection area. The transmission area is in astructure in which a portion having a symmetric relation with a portionabove the reflective layer 8, with the reflective layer 8 being aborder, is provided below the reflective layer 8. That is, the thicknessof the liquid crystal layer 3 is twice, and a ¼ wavelength plate 219 anda polarizing layer 241 (refer to FIG. 3) are provided at the back sideof the back substrate 2.

FIG. 5 is a perspective view showing an example of a portableinformation terminal device in which the image display apparatusaccording to the present invention has been incorporated.

A personal digital assistant (PDA) 300 has a compact structure with anoperating unit 311 by which commands are inputted, a processing unit 310for processing information in accordance with the commands, and adisplay unit 320 for displaying the processed information beingintegrally incorporated.

The processing unit 310 has basic functions as a PDA, and typicallyincludes a communication section, an audio processor, a controller, astorage section, etc. As a central processing unit (CPU) controls thesefunctions, the PDA 300 implements a telephone function, an electronicmail function, a personal computer function, a PC communicationfunction, a personal information managing function, etc. By operatingthe operating unit 311, the user can select a variety of functions. Theprocessing unit 310 generates image information in accordance with thecontents of the processing to be executed.

The display unit 320 displays the image information generated in theprocessing unit 310. This display unit 320 comprises a display panelhaving pixels arranged in a matrix form and displaying images byreflecting external light from the front side or by having illuminationlight from the back side transmit therethrough, and a flat-type backlight arranged at the back of the display panel and radiating theillumination light. Each pixel is divided on a flat surface into areflection area for reflecting the external light incident from thefront side of the display panel to display an image and a transmissionarea for transmitting the illumination light incident from the back sideof the display panel to display an image. The back light is a flat type,with layers consisting of electrodes and a luminescent layer sandwichedinbetween being formed on a substrate, and radiates the illuminationlight generated from the luminescent layer toward the transmission areaof each pixel when voltage is applied between the upper and lowerelectrodes.

An image display apparatus incorporating a hybrid-type display panel anda flat back light utilizing a self luminous element such as an organicEL is particularly applicable to a display in a portable informationterminal device. As for a back light, a self luminous element is used,and thus its thickness can be reduced compared with that of aconventional back light, and the luminous efficiency can be improved.Also, as the back light is used with the hybrid-type display panel, itdoes not need to be lit while external light is available, thus toreduce electric power consumption. In particular, when the apparatus ismanufactured so that a luminescent light may be supplied only to thetransmission area of the display panel, it is possible to reduceelectric power consumption to a large extent.

FIG. 6 is a schematic plan view showing an example of a portabletelephone terminal device in which the image display apparatus accordingto the present invention has been incorporated.

The portable telephone terminal device has a compact structure with anoperating unit for basically allowing a user to perform operations ontransmission and reception, a speech unit for allowing the user to speakin accordance with the operations, and a display unit enabling todisplay at least information on the operations being integrallyincorporated.

Specifically, a the portable telephone terminal device 400 comprises anantenna 431 for wireless transmission, a receiver (loudspeaker) 432, atransmitter (microphone) 433, operation keys 434 such as dial keys andan image display unit (display unit) 435, as shown in FIG. 6. Thisportable telephone terminal device 400 can display telephone directoryinformation such as personal names and phone numbers on the display unit435. In some cases, the device 400 may display received electronic mailson the display unit 435.

INDUSTRIAL APPLICABILITY

As described above, in the present invention, a hybrid-type displaypanel and a back light utilizing a self luminescent material are usedtogether. A self luminescent material is exemplified by an organic EL.As the self luminescent material is used for the back light, thethickness of the flat-type back light can be reduced, and thus thethickness of the display module itself can be reduced. Thus, theapparatus of the present invention is applicable particularly to adisplay unit for a portable information terminal device and a portabletelephone terminal device.

The display panel is a hybrid type, with a reflection area and atransmission area being provided together for each pixel, and externallight can be used as well as illumination light from the back light,thus to reduce electric power consumption. Thus, the apparatus of thepresent invention is applicable to a display unit for a portable device.Especially, the shape of the luminescent area of the back light matchesthat of the transmission area of the display panel, which leads toreduction of the electric power consumption.

1. An image display apparatus comprising: a display panel having pixelsarranged in a matrix form and displaying images by reflecting externallight from the front side or by having illumination light from the backside transmit therethrough; and a flat-type back light arranged at theback of the display panel and radiating the illumination light, wherein,each pixel is divided on a flat surface into a reflection area forreflecting the external light incident from the front side of thedisplay panel to display an image and a transmission area fortransmitting the illumination light incident from the back side of thedisplay panel to display an image, the transmission area beingpositioned within a perimeter of the reflection area along the flatsurface; the back light is a flat type with a substrate on which areformed layers consisting of a bottom electrodes, a top electrode, and aluminescent layer sandwiched inbetween the top and bottom electrodes,the back light radiating the illumination light generated from theluminescent layer toward the transmission area of each pixel whenvoltage is applied between the electrodes, and the top electrode havinga shape that matches and is aligned with the shape of the transmissionarea.
 2. The image display apparatus according to claim 1, wherein theluminescent layer is composed of an organic electro-luminescentmaterial.
 3. The image display apparatus according to claim 1, whereinthe display panel comprises a pair of upper and lower substrates on eachof which is formed an electrode, and liquid crystal held between thesubstrates.
 4. The image display apparatus according to claim 3, whereinthe back light has a polarizing layer deposited on the layers consistingof the top and bottom electrodes and the luminescent layer sandwichedinbetween the top and bottom electrodes, and the liquid crystal displaysan image, effected by the illumination light transmitted through thepolarizing layer.
 5. A method for manufacturing an image displayapparatus including a display panel having pixels arranged in a matrixform and displaying images by reflecting external light from the frontside or by having illumination light from the back side transmittherethrough and a flat-type back light arranged at the back of thedisplay panel and radiating the illumination light, the methodcomprising: a display panel preparation step of preparing the displaypanel by integrating on a substrate pixels each of which is divided on aflat surface into a reflection area for reflecting the external light todisplay an image and a transmission area for transmitting theillumination light to display an image, said display panel preparationstep including the step of positioning the transmission area within aperimeter of the reflection along said flat surface; a back lightpreparation step of preparing the flat-type back light by forming on asubstrate layers consisting of a bottom electrode, a top electrode, anda luminescent layer sandwiched inbetween the top and bottom electrodes;and an assembly step of assembling the back light on the back surface ofthe display panel so that the illumination light generated from theluminescent layer can be radiated toward the transmission area of eachpixel when voltage is applied between the electrodes, wherein in theback light preparation step, the top electrode has a shape that matchesand is aligned with the shape of the transmission area.
 6. The methodfor manufacturing an image display apparatus according to claim 5,wherein in the back light preparation step, an organicelectro-luminescent material is used as the luminescent layer.
 7. Themethod for manufacturing an image display apparatus according to claim5, wherein in the display panel preparation step, a pair of upper andlower substrates to each of which is formed an electrode face to eachother at a predetermined space, and liquid crystal is held in the space.8. The method for manufacturing an image display apparatus according toclaim 7, wherein in the back light preparation step, a polarizing layeris deposited on the layers consisting of the top and bottom electrodesand the luminescent layer sandwiched inbetween, and the liquid crystaldisplays an image, effected by the illumination light transmittedthrough the polarizing layer.
 9. A portable information terminal deviceintegrally incorporating an operating unit by which commands are input,a processing unit for processing information in accordance with thecommands, and a display unit for displaying the processed information,wherein: the display unit includes a display panel having pixelsarranged in a matrix form and displaying images by reflecting externallight from the front side or by having illumination light from the backside transmit therethrough, and a flat-type back light arranged at theback of the display panel and radiating the illumination light; eachpixel is divided on a flat surface into a reflection area for reflectingthe external light incident from the front side of the display panel todisplay an image and a transmission area for transmitting theillumination light incident from the back side of the display panel todisplay an image, the transmission area being positioned within aperimeter of the reflection area along the flat surface; and the backlight is a flat type, with layers consisting of a bottom electrode, atop electrode, and a luminescent layer sandwiched inbetween being formedon a substrate, and radiates the illumination light generated from theluminescent layer toward the transmission area of each pixel whenvoltage is applied between the electrodes, wherein the top electrodehave a shape that matches and is aligned with the shape of thetransmission area.
 10. The portable information terminal deviceaccording to claim 9, wherein the luminescent layer is composed of anorganic electro-luminescent material.
 11. The portable informationterminal device according to claim 9, wherein the display panelcomprises a pair of upper and lower substrates to each of which isformed an electrode, and liquid crystal held between the substrates. 12.The portable information terminal device according to claim 11, whereinthe back light has a polarizing layer deposited on the layers consistingof the top and bottom electrodes and the luminescent layer sandwichedinbetween, and the liquid crystal displays an image, effected by theillumination light transmitted through the polarizing layer.
 13. Aportable telephone terminal device integrally incorporating an operatingunit for allowing a user to perform operations on transmission andreception, a speech unit for allowing the user to speak in accordancewith the operations, and a display unit enabling to display at leastinformation on the operations, wherein: the display unit includes adisplay panel having pixels arranged in a matrix form and displayingimages by reflecting external light from the front side or by havingillumination light from the back side transmit therethrough, and aflat-type back light arranged at the back of the display panel andradiating the illumination light, each pixel being divided on a flatsurface into a reflection area for reflecting the external lightincident from the front side of the display panel to display an imageand a transmission area for transmitting the illumination light incidentfrom the back side of the display panel to display an image, thetransmission area lying within a perimeter of the reflection area alongthe flat surface, the back light being a flat type, with a substrate onwhich are formed layers consisting of a bottom electrode, a topelectrode, and a luminescent layer sandwiched inbetween, backlightradiating the illumination light generated from the luminescent layertoward the transmission area of each pixel when voltage is appliedbetween the electrodes, and the top electrode have a shape that matchesand is aligned with the shape of the transmission area.
 14. The portabletelephone terminal device according to claim 13, wherein the luminescentlayer is composed of an organic electro-luminescent material.
 15. Theportable telephone terminal device according to claim 13, wherein thedisplay panel comprises a pair of upper and lower substrates to each ofwhich is formed an electrode, and liquid crystal held between thesubstrates.
 16. The portable telephone terminal device according toclaim 15, wherein the back light has a polarizing layer deposited on thelayers consisting of the top and bottom electrodes and the luminescentlayer sandwiched inbetween, and the liquid crystal displays an image,effected by the illumination light transmitted through the polarizinglayer.